Electronic Structure, Localization and 5 f Occupancy in Pu Materials
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Electronic Structure, Localization and 5f Occupancy in Pu Materials Miles F. Beaux II, John J. Joyce, Tomasz Durakiewicz, Kevin S. Graham, Eric D. Bauer, Jeremy N. Mitchell, Paul H. Tobash, and Scott Richmond1 1
Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.
ABSTRACT The electronic structure of delta plutonium (G-Pu) and plutonium compounds is investigated using photoelectron spectroscopy (PES). Results for G-Pu show a small component of the valence electronic structure which might reasonably be associated with a 5f 6 configuration. PES results for PuTe are used as an indication for the 5f 6 configuration due to the presence of atomic multiplet structure. Temperature dependent PES data on G-Pu indicate a narrow peak centered 20 meV below the Fermi energy and 100 meV wide. The first PES data for PuCoIn5 indicate a 5f electronic structure more localized than the 5fs in the closely related PuCoGa5. There is support from the PES data for a description of Pu materials with an electronic configuration of 5f 5 with some admixture of 5f 6 as well as a localized/delocalized 5f 5 description. INTRODUCTION The complexity of the electronic structure for Pu materials arises from the open 5f electron shell which sits at the boundary between localized and delocalized electron character. This dual nature of the 5f electrons may be explored by putting the Pu atom in different electronic environments determined by ligands, lattice constants and crystal structures. Following this approach to systematics in Pu electronic structure, the Pu metal alpha (D) to delta (G) phase transition represents the best known example of Pu in a changing solid state environment with a 25% lattice expansion between the D and G phases. A great deal of effort has been expended measuring and calculating the electronic structure of both G and D Pu [1-7]. Looking to understand Pu and actinide electronic structure through systematics associated with related families of materials, a prime example is the monochalcogenides PuX (X= S, Se, Te) [8-12]. Another related family is AnTe (An= U, Np, Pu) [13]. In these systematic studies the crystal structure is held constant along with very small variations in lattice constant while the ligand or actinide is varied. It was found that within the PuX family there was a common electronic structure component composed of three peaks within the first 1 eV of binding energy which corresponded well to predictions of the atomic multiplet theory with a 5f 6 initial state for the Pu f-electrons [14]. The PuX family shows more 5f 6 character than other Pu materials, and a rigorous determination of the valence for these materials is still an active area of research, with a range generally accepted between 5.5 and 6. Comparing G-Pu to PuTe provides an opportunity to explore the balance between Pu 5f 5 and 5f 6 electronic configurations. More recently, a family of Pu superconductors was discovered including the 18.5 K superconductor PuCoGa5 [15] and a new 2.5 K superconductor PuCoIn5 [16]. These two materials have the s
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